1. Technical Field
The present invention relates to an optical reflecting device used for a display apparatus or the like.
2. Background Art
Conventional optical reflecting device 1 is shown in FIG. 10. As shown in FIG. 10, conventional optical reflecting device 1 includes fixed frame 2, one pair of first oscillation parts 3 and 4, movable frame 5, one pair of second oscillation parts 6 and 7, and mirror part 8. One-side ends of one pair of first oscillation parts 3 and 4 are connected to the inside of fixed frame 2. Movable frame 5 is connected to and held by the other-side ends of one pair of first oscillation parts 3 and 4. One-side ends of one pair of second oscillation parts 6 and 7 are connected to the inside of movable frame 5 and are disposed to be substantially perpendicular to one pair of first oscillation parts 3 and 4. Mirror part 8 is connected to and held by the other-side ends of one pair of second oscillation parts 6 and 7 to be pivotable. Movable frame 5 is pivoted around the X axis (X1 axis) which is passing through the substantial center of mirror part 8 and along one pair of first oscillation parts 3 and 4. Mirror part 8 is pivoted around the Y axis (Yl axis) which is passing through its center and along one pair of second oscillation parts 6 and 7. Thus, optical reflecting device 1 scans a light flux (light spot) radiated and reflected from mirror part 8 in the X and Y axis directions and projects an image onto a screen.
FIG. 11 is an enlarged perspective view illustrating second oscillation part 7. As shown in FIG. 11, second oscillation part 7 has a so-called meandering shape in which a beam is folded a plurality of times. Second oscillation part 7 includes a plurality of straight portions 9a and a plurality of folded portions 9b formed by folding the plurality of straight portions 9a. 
A driving element such as a piezoelectric body is formed in each of the plurality of straight portions 9a. In second oscillation part 7, large displacement of mirror part 8 is realized by driving the driving elements so that the phases of the driving elements are opposite to each other and by displacing and bending straight portions 9a in arrow directions so that the amount of displacement accumulates according to the number of straight portions 9a, as shown in FIG. 12.
For example, the optical reflecting device of the application is disclosed in, for example, PLT 1.
To improve the resolution of a projected image, the scanning speed of a light flux (light spot) needs to be increased by increasing a driving frequency while maintaining the amount of displacement of each oscillation part. In this case, however, there is a problem that stress is focused on the folded portions of each oscillation part and thus crack or the like easily occurs.